The invention is directed to optimal view strategies for cardiac interventional treatment planning, and, more particularly relates to the generation and use of a feasibility map for modeling vascular characteristics of a patient in view of physical constraints, such as a 3D coronary artery tree, prior to and/or concurrently with intervention.
Quantitative description of the coronary arterial tree including geometry is required for diagnosis and prognosis of coronary disease, as well as for performance of catheter-based coronary interventions. Many computer-assisted techniques for estimation of the three-dimensional (3-D) coronary arteries from biplane projection are known in the art. However, due to the problem of vessel overlap and foreshortening, multiple projections are necessary to adequately evaluate the coronary arterial tree with arteriography. The elimination or at least minimization of foreshortening and overlap is a prerequisite for an accurate quantitative coronary analysis (QCA), such as determination of intercoronary lengths in a 2-D display.
Optimal view maps (OVMs) are known in the art. OVMs aid a user in obtaining a gantry position of the imaging device which results in an optimal view; OVMs were devised in an effort to remove the subjective nature of minimizing foreshortening and overlap. For example, G. Finet and J. Lienard, OPTIMIZING CORONARY ANGIOGRAPHIC VIEWS, Int. Journal Cardiac Imaging, Supplement 1, vol. 1, pp. 53-54, 1995, focused only on minimization of vessel foreshortening relative to a single arterial segment.
Y. Sato, et al., A VIEWPOINT DETERMINATION SYSTEM FOR STENOSIS DIAGNOSIS AND QUANTIFICATION IN CORONARY ANGIOGRAPHIC ACQUISITION, IEE Tran. On Medical Imaging, vol. 17, no. 1, pp. 53-54, 1995, and S. J. Chen and J. D. Caroll, 3-D CORONARY ANGIOGRAPHY: IMPROVING VISUALIZATION STRATEGY FOR CORONARY INTERVENTIONS, Whats New In Cardiovascular Imaging, Kluwer Academic Publishers, pp. 61-67, 1998 (Chen and Carroll I), discuss derivation of an optimal view strategy on the basis of minimization of both vessel overlap and foreshortening. However, the technique devised by Sato requires a well-calibrated imaging system and manually specified correspondence in the 3-D reconstruction process. Additionally, the overlap measurement is limiting because it is performed based on the single stenotic segment with only immediate adjacent vessels. Sub-optimal solutions in determining optimal view are ineffective when the segment was more complex and more distal vessels were overlapped, both conditions of which are common in clinical conditions.
Broadly, conventional OVMs are utilized for on-line reconstruction of a 3D arterial tree based on a pair of routine angiograms acquired from any two arbitrary viewing angles using single- of bi-plane imaging systems. A conventional process for deriving an OVM requires 1) acquisition of two standard angiogram sequences by use of a single-plane imaging system; 2) identification of 2D arterial tress and feature extractions, including bifurcation points, vessel diameters, vessel directional vertices, vessel centerlines, and construction of vessel hierarchies in the two images; 3) determination of a transformation defining the spatial relationship of the acquired two views in terms of a rotation matrix and translation vector; and 4) calculation of the 3D arterial (e.g., coronary) trees arterial structures based thereon. S. J. Chen and J. D. Caroll, 3-D RECONSTRUCTION OF CORONARY ARTERIAL TREE TO OPTIMIZE ANGIOGRAPHIC VISUALIZATION, IEEE Transactions on Medical Imaging, vol. 19, no. 4, April, 2000 (hereafter “Chen and Carroll II”), incorporated herein by reference.
The Chen and Carroll II 2-view approach does require considerable manual editing in order to retrieve the coronary tree. As used hereinafter, the more general term ‘modeling’ shall be used to describe techniques which are similar to the above-described 2-view approach in that they are aimed at the construction of a schematic description of the coronary tree based on several image data acquisitions. More particularly, Chen and Carroll II teaches the use two types of optimal view maps, the foreshortening map and the overlap map, which two map types may be combined by the user to form a composite map, i.e., the 2-View map. Prior art FIGS. 1(a) and 1(b) show the extracted features including vessel diameter, bifurcation points, direction vectors and vessel centerlines of the left coronary arterial tree.
Chen and Carroll II also teaches that an on-line 3-D reconstruction technique to reconstruct the entire coronary arterial trees based on two views required from routine angiograms without need of a calibration object, and using a single-plane imaging system, as well as a new optimization algorithm realized by minimizing the image point and vector angle errors in both views subject to constraints derived from the intrinsic parameters of the single-plane imaging system.
Given the 3-D character of the coronary artery tree, Chen and Carroll II expected that any projection would foreshorten a variety of segments. A reconstructed 3-D coronary arterial tree may be rotated to any selected viewing angle yielding multiple computer-generated projections to determine for each patient which standard views are useful and which have no clinical value due to excessive overlap and foreshortening. Chen and Carroll II provide for computer-simulated projections for display with information of calculated percent foreshortening and overlap on the screen, such that a used may select any view by use of keyboard input.
The foreshortening map is an interactive map created as a composite of viewable sizes of the central vessel axis of a segment of interest for all possible viewing angles. Use of the foreshortening map renders a user able to manually explore suggested viewing positions and to manipulate the vessel model and check the corresponding position on the foreshortening map. The displayed size of the vessel or luminary organ of interest depends on the actual viewing direction of the coronary tree with respect to the position of the radiation source.
In prior art FIG. 2(a), the white arrow is arranged to point towards a manually determined coronary segment of interest. The corresponding central vessel axis is shown as a black line. Prior art FIG. 2 (b) is an example of a conventional foreshortening map, which foreshortening map may be color-coded to provide a quick and intuitive overview of the viewing angles and corresponding gantry positions. Foreshortening maps minimize amounts of foreshortening, allowing for manual exploration of suggested viewing angles. An example of an optimal viewing angle for viewing a particular vessel of luminary organ is shown in prior art optimal view map of FIG. 2(c).
Next to a possible foreshortening, it is also possible that other vessel segments are overlapping the segment of interest, which case is clear by way of view shown in prior art FIG. 3(a). As a result, the operator may want to find another viewing angle in order to obtain a more clear sight (or view) of the vessel or other lumen of interest. This type of map is referred to in the conventional arts as an overlap map. Such an overlap map provides that for every possible viewing angle an estimate may be made of how much overlap is actually present. This information is preferably color-coded, such as is set forth in an interactive table comprising FIG. 3(b). An example of the optimal viewing angle is shown in the prior art optimal view map of FIG. 3(c) (overlap).
Chen and Carroll further investigated and developed the work set forth in Chen and Carroll I. S. J. Chen and J. D. Caroll, COMPUTER ASSISTED CORONARY INTERVENTION BY USE OF ON-LINE 3D RECONSTRUCTION AND OPTIMAL VIEW STRATEGY, MICCAI 1998:377-385 (hereafter “Chen and Carroll III”), incorporated herein by reference. Said further investigation realized the use of a composite map in addition to the foreshortening and overlap map. The coronary treatment disclosed in Chen and Carroll III sets forth a process which includes selecting an arterial segment of interest on the projection of the reconstructed 3D coronary model (for example, at an identified arterial stenosis or any veinous or non-vascular lumenary pathway blockage). Based thereon, their suggested optimal view strategic process is employed to realize a foreshortening, an overlap and a composite map.
The Chen and Carroll III composite map comprises a combination of the foreshortening and overlap maps discussed above. The maps utilized by Chen and Carroll III enable a user to interactively select arterial segments by which any computer-generated projection image associated with the gantry orientation may be previewed. More particularly, the two maps together, formed as a composite map, are said to facilitate views with minimal foreshortening and vessel overlap for the selected arterial segment in order to guide subsequent angiographic acquisitions for interventional processes.
While the Chen and Carroll III developments provide significant support for 3D viewing, selection of optimal viewing angles using their process may still present problems for the viewer, the problem becoming particularly acute when their process is used in a real-time intervention. That is, using the Chen and Carroll III view map may still limit a viewer's ability to clearly and effectively discern the position of a gantry used in image data acquisition and Chen and Carroll's foreshortening, overlap and composite maps.